Synthesis and Oxidation Testing of MAX Phase Composites in the Cr-Ti-Al-C Quaternary System.

According to the properties determined for the ternary end-members, MAX phases in the quaternary Cr-Ti-Al-C system could be of interest as protective coatings for nuclear fuel cladding in the case of severe accident conditions. In this study, syntheses of 211 and 312 MAX phase compositions were attempted using pressureless reactions starting from Cr, TiH2, Al, and C (graphite) powders. It was observed that both the Ti substitution by Cr in Ti3AlC2 and the mutual solubility of Ti2AlC and Cr2AlC are limited to a few atomic percent. In addition, the remarkable stability of the (Cr2/3Ti1/3)3AlC2 MAX phase composition was confirmed. Due to the low miscibility of MAX phases in the Cr-Ti-Al-C system, most samples contained substantial amounts of TiC x and Al-Cr alloys as secondary phases, thus forming composite materials. After sintering, all samples were submitted to a single oxidation test (12 h at 1400°C in air) to identify compositions potentially offering high-temperature oxidation resistance and so warranting further investigation. In addition to (Cr0.95Ti0.05)2AlC, composite samples containing substantial quantities of Al8Cr5 and AlCr2 formed a stable and passivating Al2O3 scale, whereas the other samples were fully oxidized. [ABSTRACT FROM AUTHOR]